Cooking device having stirrer movable about two mutually perpendicular axes

ABSTRACT

A domestic cooking system including a base defining one or more cooking locations, electromagnetic induction apparatus for heating a food at the cooking location and apparatus for automatic stirring of the food at the cooking location.

FIELD OF THE INVENTION

The present invention relates to domestic food cooking apparatus andsystems generally.

BACKGROUND OF THE INVENTION

Various types of domestic food cooking apparatus are known in the art.In the domestic cooking art, there are known various automated cookingdevices including mechanical mixing apparatus.

The following patents are considered to be representative of the priorart:

U.S. Pat. No. 3,635,147 describes a combination cooking-stirring vesselin which two sets of blades are rotated continuously by means of a motordrive applied to the rim of a generally round bowl, as food is heated.One set of blades rotates along the bottom of the bowl except at thecenter bottom region.

U.S. Pat. No. 1,790,115 describes apparatus for treating food productscomprising a plurality of rotating blades and a curved bottom surface.

U.S. Pat. No. 4,693,610 describes an electrical household appliance forculinary purposes including apparatus for stirring and heating thecontents of a bowl. This apparatus provides continuous rotation of astirrer adjacent the bottom of a flat bottomed bowl.

U.S. Pat. No. 4,649,810 describes microcomputer-controlled integratedcooking apparatus for automatically preparing culinary dishes. Theapparatus includes a memory for storing one or more recipe programs. Therecipe program specifies schedules for dispensing the ingredients from acompartmentalized carousel into a flat bottomed cooking vessel, forheating the vessel and for continuously stirring the contents of thevessel.

U.S. Pat. No. 1,491,991 describes a beverage mixer and heater whichprovides stirring of the contents of a container having an electricheating element incorporated in its construction.

In an industrial environment, which is distinct from the domestic foodcooking field discussed above, there have been proposed various deviceswhich provide heating or cooling of food products. For example, U.S.Pat. No. 4,073,225 describes, on an industrial scale, a continuouslyoperable meatball cooker employing a trough which is engaged by helicalvanes. U.S. Pat. No. 3,407,872 employs a trough-like tank having areciprocating paddle for circulating a heating or cooling fluid.

Italian patent 567138, granted Oct. 1, 1957, describes a mechanicalagitator including first and second series connected mutually angledshafts, which are driven by a motor. The second shaft includes a fixedtermination end which engages the inner surface of a container.

U.S. Pat. No. 4,629,843 describes induction cooking apparatus having aferrite coil support and includes monitoring and control apparatus forpreventing heating of the ferrite coil support above its Curietemperature.

U.S. Pat. No. 4,467,162 describes an arrangement for an inductionheating process employing a shielding plate member of non-magnetizablemetallic material disposed in a space between a heating coil and abottom plate.

U.S. Pat. No. 3,761,668 describes a cooking system wherein smallelectrical appliances are powered by an induction cooking device.

U.S. Pat. No. 4,817,510 illustrates cooking apparatus wherein thetemperature of cooked food is automatically controlled and varied duringa cooking cycle.

U.S. Pat. No. 4,885,447 describes a system for induction heating of theelectric plates of a cooker and employs an inverter bridge of MOStechnology to provide a pulsating current.

U.S. Pat. No. 4,736,082 describes electromagnetic induction heatingapparatus capable of preventing undesirable states of cooking utensilsor vessels.

U.S. Pat. No. 4,549,056 describes electromagnetic induction heatingapparatus capable of heating nonmagnetic cooking vessels and employs anAC field having a frequency of at least 50 KHz and preferably about 100KHz, for heating non-magnetic materials such as aluminum. For magneticmaterials, such as iron, a separate switching circuit and a separatecoil provide an AC field having a significantly lower operatingfrequency. U.S. Pat. No. 4,749,836 describes electromagnetic inductioncooking apparatus capable of providing a substantially constant inputpower, which includes features similar to those described above inconnection with the apparatus of U.S. Pat. No. 4,549,056.

U.S. Pat. No. 4,792,652 describes an electric induction cookingappliance with reduced harmonic emission which employs a plurality ofcoils wound in opposite senses. U.S. Pat. No. 4,453,067 describes aninduction heating coil having non-uniformly spaced turns.

U.S. Pat. No. 3,814,888 describes a solid state induction cookingappliance operating at ultrasonic frequencies.

U.S. Pat. Nos. 3,814,888; 4,296,295; 4,617,441; 4,667,074; 4,426,564;3,761,668 and 3,742,179 all show induction heating systems for cookingand some show temperature measurement apparatus operative therewith.

SUMMARY OF THE INVENTION

The present invention seeks to provide improved domestic food cookingapparatus as well as integrated, modular versatile domestic cookingsystems for quick cooking of most foods in the kitchen. The term"cooking" will be used throughout to refer generally to the applicationof heat to foodstuffs in a domestic context and includes, iter alia,heating liquids of various viscosities, and dry roasting of bulkfoodstuffs, such as nuts, beans and seeds.

It is a principal object of the present invention to provide a systemcapable of carrying out all normal domestic cooking functions within asmall area. These functions include, for example, cooking of liquids,such as soups, stews and the like, frying, roasting, baking, defrostingand boiling of water.

The cooking center of the present invention may comprise a compact unitwhich can operate interchangeably with a wide variety of cookingutensils.

According to a preferred embodiment of the invention, the cooking centeris characterized in that it provides fast and uniform cooking at highenergy efficiency. The cooking center of the present invention is easyto operate and may provide controlled cooking and even stirring offoods.

There is thus provided in accordance with an embodiment of the presentinvention a domestic cooking system useful for heating utensils having abottom surface formed of a metal having low electrical resistance, thesystem including electromagnetic induction apparatus including aninduction coil having more than 80 turns and preferably more than 100turns.

There is also provided in accordance with a preferred embodiment of thepresent invention a domestic cooking system useful for heating a utensilhaving a bottom surface formed of a metal having low electricalresistance, the system comprising electromagnetic induction apparatusincluding an induction coil receiving an AC electrical input at afrequency less than 50 KHz and preferably less than 30 KHz.

There is further provided in accordance with a preferred embodiment ofthe present invention a domestic cooking system useful for heating autensil having a bottom surface formed of a metal having low electricalresistance, the system comprising electromagnetic induction apparatusincluding an induction coil having a voltage of less than 4000 Voltsthereacross during operation.

There is additionally provided in accordance with a preferred embodimentof the present invention a domestic cooking system useful for heatingutensils having a bottom surface formed of a metal having low electricalresistance and comprising electromagnetic induction apparatus includinginduction producing apparatus producing inductance of at least 1000microHenry and preferably in excess of 2000 microHenry.

There is also provided in accordance with a preferred embodiment of thepresent invention a domestic cooking system including a base defining atleast one cooking location, electromagnetic induction apparatus forheating a food at the cooking location and apparatus for automaticstirring of the food at the cooking location.

There is additionally provided in accordance with a preferred embodimentof the present invention a domestic cooking system comprisingelectromagnetic induction apparatus for heating a food at the cookinglocation by providing magnetic flux at the cooking location andapparatus for providing electric field shielding at least between theelectromagnetic induction apparatus and the cooking location. Preferablythe apparatus for providing electric field shielding is operative tosurround the electromagnetic induction apparatus and to provideelectromagnetic shielding of the electromagnetic induction apparatus,while permitting the substantially unimpeded passage of magnetic fluxacross the electromagnetic shielding apparatus to the cooking location.

There is additionally provided in accordance with a preferred embodimentof the present invention a domestic cooking system useful for heatingutensils having a bottom surface formed of a metal having low electricalresistance, the system including electromagnetic induction apparatus forheating a food at a cooking location, the electromagnetic inductionapparatus operating in a non-resonant mode. Preferably, theelectromagnetic induction apparatus comprises an induction coil and highfrequency switching apparatus and apparatus for providing negativefeedback to the high frequency switching apparatus.

There is further provided in accordance with an embodiment of thepresent invention a domestic cooking system useful for heating utensilsof a first type, having a bottom surface having high electricalresistance, and of a second type, having a bottom surface having lowelectrical resistance, the system including:

electromagnetic induction apparatus including an induction coil;

automatic control apparatus for governing the operation of theelectromagnetic induction apparatus and being operable in first andsecond modes, the first mode being suitable for heating utensils of thefirst type and employing a first number of turns of the induction coiland the second mode being suitable for heating utensils of the secondtype and employing a second number of turns of the induction coil,larger than the first number of turns; and

apparatus for supplying an AC electrical power input to the inductioncoil generally at the same frequency during operation in both the firstand second modes.

There is also provided in accordance with a preferred embodiment of theinvention a domestic cooking system comprising:

a base defining at least one cooking location and comprisingelectromagnetic induction apparatus including:

an induction coil disposed generally in at least one plane and operativeto generate electromagnetic flux; and

at least one magnetic field conductor disposed in a plane extendinggenerally non-parallel to the at least one plane so as to directelectromagnetic flux generated by the induction coil to the at least onecooking location. Preferably the magnetic field conductor comprises aferromagnetic foil which is disposed generally perpendicular to the atleast one plane and has a ratio of width in the direction generallyperpendicular to the at least one plane relative to thickness of atleast 10 and more preferably of at least 200. Preferably theferromagnetic foil comprises a plurality of groups of generally radiallyextending foils, individual ones of said plurality of groups beingelectrically insulated from each other.

Alternatively the magnetic field conductor comprises a ferromagneticwire wound in a generally toroidal arrangement to define a plurality ofloops, each of which is disposed in a plane generally perpendicular tothe at least one plane.

Preferably, the magnetic field conductor includes portions which extendgenerally radially, comprises amorphous metal and has a thickness ofless than 0.3 mm and preferably between 0.05 and 0.10 mm.

In accordance with a preferred embodiment of the invention, the cookingsystem also comprises at least one cooking utensil defining a foodheating surface and being operative .to be heated by the electromagneticflux at the cooking location, and the magnetic field conductor isdisposed on the opposite side of the induction coil from the utensil.

In accordance with a preferred embodiment of the invention, the systemalso includes automatically operative stirring apparatus and/orapparatus for sensing the temperature of a cooking utensil at a cookinglocation. The apparatus for sensing temperature may include apparatusfor obtaining temperature information relating to a utensil fromvariations in the current passing through the induction coil.

Apparatus may be provided for controlling the supply of heat to autensil in accordance with the temperature of the utensil and mayinclude apparatus for supplying heat until the temperature of theutensil exceeds the indicated desired temperature by a first thresholdand thereafter supplying heat to maintain the difference between thetemperature of the utensil and the indicated desired temperature withina second threshold.

The apparatus for controlling may also comprise timing apparatus used tocontrol the heating apparatus.

The cooking utensil preferably includes a curved cooking surface havinga generally circular cross sectional configuration and the stirringapparatus preferably includes:

at least one stirrer arranged about a stirrer rotation axis and definingan attachment end and a termination end;

apparatus for rotating the stirrer about the stirrer rotation axis; and

apparatus for reciprocally rotating the stirrer about a reciprocalmotion axis perpendicular to the stirrer rotation axis such that thetermination end moves along the curved cooking surface.

There is also provided in accordance with a preferred embodiment of theinvention, for use with a utensil having a curved cooking surface havinga generally circular cross sectional configuration, stirring apparatuscomprising:

at least one stirrer arranged about a stirrer rotation axis and definingan attachment end and a termination end;

apparatus for rotating the at least one stirrer about the stirrerrotation axis; and

apparatus for reciprocally rotating the at least one stirrer about areciprocal motion axis perpendicular to the stirrer rotation axis suchthat the termination end moves along the curved cooking surface.

The stirrer preferably has a generally screw-type configuration. Thestirring drive apparatus preferably includes quick coupling apparatusfor automatically coupling the stirrer drive apparatus to the stirrer.The stirring drive apparatus preferably provides first and second rotarydrive outputs.

The stirring apparatus preferably includes a utensil contacting membermounted onto the termination end of the stirrer and preferably isselectably orientable with respect thereto so as to correspond to theconfiguration of the utensil surface when in engagement therewith.

There is also provided in accordance with an embodiment of theinvention, stirring apparatus including:

a stirrer having an attachment end and a termination end;

apparatus for mounting the stirrer at the attachment end and driving thestirrer in motion in operative association with a utensil defining autensil surface; and

a utensil contacting member mounted onto the termination end of thestirrer and being selectably orientable with respect thereto so as tocorrespond to the configuration of the utensil surface when inengagement therewith.

There is also provided in accordance with an embodiment of theinvention, a cooking temperature sensor for use with a domestic cookingsystem including an induction heating apparatus including an inductioncoil and apparatus for measuring temperature by sensing variations inthe current flow passing through the induction coil.

In accordance with an embodiment of the present invention there isprovided a cooking utensil formed of a metal and defining a curvedcooking surface and a heat transfer member, formed of a metal and havinga generally flat bottom surface and a curved top surface engaging theunderside of the curved cooking surface.

In accordance with a preferred embodiment of the invention, the cookingutensil is formed of a metal surface having a high electrical resistanceand the heat transfer member is formed of a metal having a lowelectrical resistance. Alternatively both elements may be formed of thesame metal.

Additionally in accordance with an embodiment of the present invention,there is provided a cooking system including the above described cookingutensil and including apparatus for providing heating of the flat bottomsurface thereof. The apparatus for providing heating may include aconventional electrical resistance heat source or alternatively aninductive heat source.

Stirring apparatus of the type described hereinabove may be employedwith the cooking utensil and the cooking system.

The various features of the embodiments described hereinabove may becombined in any suitable combination in accordance with the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description, taken in conjunction with thedrawings in which:

FIGS. 1A and 1B are respective pictorial and partially cut away frontview illustrations of a domestic cooking system constructed andoperative in accordance with a preferred embodiment of the presentinvention;

FIG. 1C is a partially cut away front view illustration of a domesticcooking system constructed and operative in accordance with anotherpreferred embodiment of the present invention;

FIG. 2 is a pictorial illustration of the use of a variety of differentcooking utensils in accordance with a preferred embodiment of theinvention;

FIG. 3 is a generalized electrical diagram of control circuitry usefulin the present invention;

FIGS. 4A, 4B, 4C, 4D, 4E and 4F are electrical schematic illustrationsof the control circuitry of FIG. 3;

FIG. 5 is a flow chart illustrating the operation of the controlcircuitry of FIGS. 3 and 4;

FIG. 6 is an exploded view illustration of induction heating apparatusconstructed and operative in accordance with a preferred embodiment ofthe present invention;

FIG. 7A is a top plan view illustration, of a foil assembly forming partof the embodiment of FIG. 6;

FIGS. 7B, 7C, 7D, 7E, 7F, 7G and 7H are top view illustrations ofalternative embodiments of a magnetic field conductor useful in theembodiment of FIG. 6;

FIG. 7I illustrates an enlarged portion of the foil assembly of FIG. 7A.

FIG. 8 is a side view illustration of a stirring assembly constructedand operative in accordance with a preferred embodiment of the presentinvention;

FIGS. 9A and 9B are plan view and edge view illustrations of a stirringcoupler constructed and operative in accordance with a preferredembodiment of the present invention;

FIGS. 10A, 10B and 10C are three illustrations of stages in theengagement of part of the stirring assembly of FIG. 8 with the couplerof FIGS. 9A and 9B;

FIGS. 11A and 11B are respective side and plan view illustrations ofstirring drive apparatus useful in association with the apparatus ofFIGS. 8-10C;

FIG. 12 is a pictorial illustration of a stirrer particularly useful inthe apparatus of FIG. 8;

FIGS. 13A, 13B and 13C are pictorial illustrations of three typicalorientations of a utensil contacting member relative to the terminationend of a stirrer, such as that of FIG. 12;

FIG. 14 is a sectional illustration of an alternative embodiment ofutensil contacting member; and

FIG. 15 is a diagrammatic illustration of the area coverage produced byoperation of the stirring apparatus of FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

Reference is now made to FIGS. 1A and 1B which illustrate a cookingsystem constructed and operative in accordance with a preferredembodiment of the present invention and comprising a cooking center 10,including a back portion 12 and a base portion 14, defining a pluralityof cooking locations 16, each arranged for operative association with acooking utensil 18. Preferably the top surface of base portion 14 isformed of ceramic glass.

The back portion 12 and the base portion 14 comprise various controlsfor each of the cooking locations 16, such as on-off, temperature andtiming controls which may be embodied, for example, in a switch 19 withassociated indicator light, a keyboard 20 and a dial 21. A statusdisplay 22, such as an LCD display, may also be provided. Also mountedon back portion 12 is a coupler 23 of a stirrer drive assembly, which isnot seen in FIGS. 1A-1B, insofar as it is located at the interior ofback portion 12.

The base portion 14 typically defines four cooking locations. Eachcooking location is typically provided with induction heating apparatus25, which is not seen in FIG. 1A inasmuch as it is located within base14.

In the embodiment of FIGS. 1A and 1B, for the sake of illustration, allof the cooking locations are provided with induction heating apparatus,although this need not be the case.

In FIG. 1B, which represents a section taken along the lines B--B inFIG. 1A, cooking utensils formed of high resistance electricallyconductive materials, such as iron and stainless steel, and of lowresistance electrically conductive materials, such as aluminum, may beemployed. For the purposes of the present application, the term "highresistance" refers to materials having an electrical resistance withinthe general range extending from 0.05 ohm mm² /meter and higher, andpreferably at least 0.1 ohm mm² /meter and including iron at 0.1 ohm mm²/meter and stainless steel, typically at 0.72 ohm mm² /meter. The term"low resistance" refers to materials having an electrical resistancewithin the general range below 0.05 ohm mm² /meter and preferably below0.03 ohm mm² /meter and including aluminum at 0.0285 ohm mm² /meter andcopper at 0.0175 ohm mm² /meter.

A preferred embodiment of the induction heating apparatus 25 isillustrated in FIG. 6 and comprises an induction coil 26 comprising anelectrical conductor which carries a current flow and is typically, butnot necessarily, in the form of one or more coils, which lie in a singleplane or alternatively in a plurality of generally parallel planes.Preferably associated with induction coil 26 and lying thereover andthereunder are layers of electrical insulation 28, which may becontinuous or alternatively apertured, the apertures being configuredand arranged as illustrated in FIG. 6, in order to provide an air flowpath therepast, which may be useful when a ventilator (not shown) isprovided in base portion 14. Disposed under coil 26 is a magnetic fieldconductor assembly 30, various embodiments of which are illustrated inFIGS. 7A-7H.

In accordance with a preferred embodiment of the invention, shieldingapparatus 29 is disposed between induction coil 26 and cooking location16 for providing electric field shielding therebetween withoutappreciably reducing the magnetic flux provided to the cooking locationand without being itself heated to an unacceptable degree. Preferablyapparatus 29 is operative to surround the induction heating apparatusand to provide electromagnetic shielding thereof, while permitting thesubstantially unimpeded passage of magnetic flux thereacross to thecooking location.

According to one embodiment of the invention, the shielding apparatus 29is formed of expanded stainless steel mesh. According to an alternativeembodiment of the invention, the apparatus 29 is formed of a woven ornon-woven fabric including conductive fibers, such as carbon or metalfibers. Alternatively non-conductive fibers which are coated with aconductive coating may be employed.

According to one preferred embodiment of the invention, suitable forheating cooking utensils having aluminum bottom surfaces, the coil 26has an inner diameter of 40 mm, an outer diameter of 170 mm and athickness of 5.2 mm. In this example, the coil has 120 turns and isformed of Litz wire, which is formed of 96 individually lacqueredfilaments, each of 0.13 mm diameter. Preferably, during operation, avoltage of about 2000 volts AC is provided across coil 26 at anoperative frequency of 22 KHz, providing, together with magnetic fieldconductor assembly 30, an inductance of about 3400 microHenry.

As seen particularly in FIG. 7A, the magnetic field conductor assembly30, in accordance with a preferred embodiment of the invention,comprises an array of foils of a magnetic field conductive material,which are arranged to lie non-parallel and preferably generallyperpendicularly to the plane or planes of the induction coil 26, so asto minimize the generation of eddy currents in the foils.

Preferably the magnetic field conductors are formed of a highpermeability material, such as an amorphous metal, and are typicallyeach of thickness 0.025 mm. Some preferred materials are Ultraperm 10,Permenorm (5000 H2 and 5000Z) and Vitrovac 4040, all of which arecommercially available from Vacuumschmelze of Human, West Germany.

In the preferred embodiment, illustrated in FIGS. 7A and 7I, a pluralityof separate foils 32, each separated from the adjacent foil by aninsulator 34, are arranged to define radially extending sub-assemblies36, which extend radially outward from the center of the assembly. Thefoils are typically retained in position by an insulative retaining ring38, which may be provided at any suitable radial distance from thecenter of the assembly.

According to a preferred embodiment of the invention, each of foils 32has a ratio of width in the direction generally perpendicular to theplane of the induction coil 26 relative to thickness in the plane of theinduction coil of at least about 10 and preferably at least about 200. Apreferable ratio is 600.

According to an alternative embodiment of the invention, illustrated inFIG. 7B, each adjacent two sub-assemblies 36 are in fact defined by asingle plurality of foils, which is bent adjacent the center of theassembly, as indicated at reference numeral 40.

According to a further alternative embodiment of the invention,illustrated in FIG. 7C, all of the sub-assemblies 36 are togetherdefined by a single plurality of foils which extends intermittently bothradially and circumferentially.

According to a further alternative embodiment of the invention,illustrated in FIG. 7D, one or a plurality of foils is arranged in acontinuous undulating generally parallel array 41 having an overallgenerally square configuration. In FIG. 7E, an undulating array 43 hasan overall generally circular configuration, underlying coil 26.

In FIGS. 7F and 7G, an array of separate parallel foils or groups offoils is provided. In FIG. 7F, the overall configuration of the array 45is square, while in FIG. 7G, the overall configuration of the array 47is circular and conforms to the configuration of coil 26.

In accordance with a further alternative embodiment of the presentinvention, illustrated in FIG. 7H, the magnetic field conductor assembly30 may comprise a ferromagnetic wire 48 wound in a generally toroidalarrangement to define a plurality of loops 49, each of which is disposedgenerally in a plane generally perpendicular to the plane of coil 26.

It is a further particular feature of the present invention that theinductively heated cooking utensil need not necessarily have a flatbottom surface or a flat food cooking surface.

It is a particular feature of the invention that the magnetic fluxproduced by induction coil 26 in response to passage of suitable currenttherethrough is spatially defined by the utensil 18 and by magneticfield conductor assembly 30. The use of thin foils 32 or loops extendinggenerally non-parallel and preferably generally perpendicularly to theplane of the induction coil 26 instead of a thicker body offerromagnetic material lowers the heating of the induction heatingapparatus 25 as compared with the heating which would occur in arelatively thicker body of ferromagnetic material, such as ferrite,particularly if oriented parallel to the plane of the coil, thusincreasing efficiency and inductance.

It is a particular feature of the present invention that foils 32 orwire 48 are formed of a material, such as amorphous metal, which has arelatively high Curie temperature and high permeability, especially atthe operating frequency of induction heating apparatus 25, typically 22KHz.

Reference is now made to FIG. 1C, which illustrates a system which isgenerally similar to that of FIG. 1B, except as described hereinbelow.In the embodiment of FIG. 1C, the cooking utensil 13 is formed of ametal and defines a curved cooking surface 15. There is also provided aheat transfer member 17, formed of a metal and having a curved topsurface engaging the underside of the curved cooking surface and agenerally flat bottom surface.

In accordance with a preferred embodiment of the invention, the cookingutensil 13 is formed to have a metal surface having a high electricalresistance and the heat transfer member 17 is formed of a metal having alow electrical resistance. This structure is particularly suitable foruse with induction heating apparatus, such as that illustrated atreference number 25 in FIG. 1C. Alternatively both elements 13 and 17may be formed of the same metal. This alternative arrangement issuitable for use with a conventional resistance heating element,indicated by reference numeral 24. If a conventional resistance heatingelement is employed, the utensil may be formed of any suitable material,which need not necessarily be metal.

Induction heating apparatus 25 is generally similar to that shown inFIG. 1B and described hereinabove. It may, however, be modified as willnow be described. These modifications may also be employed wheresuitable in the various other embodiments of the invention described inthe specification. Vibration absorbing apparatus 27 is preferablyprovided between the induction heating apparatus 25 and both the top andbottom surfaces of the base portion 14. Additionally, the top surface ofthe base portion 14 above each cooking location may be vibrationallydecoupled from the remainder of the top surface of the base portion.

Reference is now made to FIG. 2 which illustrates the modularity andflexibility of the cooking system of the present invention, wherein asingle cooking location may alternatively accommodate a plurality ofdifferent utensils having different configurations, including, forexample, both flat and curved bottom surfaces. In accordance with apreferred embodiment of the invention, utensils having bottom surfacesof either high or low electrical resistance, such as copper andaluminum, may be used with the present invention.

The utensils usable with the present invention include both specialpurpose utensils including stirring apparatus as well as entirelyconventional cooking utensils, such as those seen in FIG. 2.

Control apparatus employed in the cooking center is illustrated in FIG.3 and includes user interface apparatus 50, typically incorporatingswitch 19, keyboard 20 and dial 21 (FIG. 1A), which provide controlinputs relating to desired cooking time and desired temperature tocontrol circuitry 52. Control circuitry 52 also receives a temperatureinput from temperature sensing apparatus 54 and provides a triggeroutput to induction heating assembly 56, a stirring control output to astirring assembly 58, described hereinbelow, and a display output to adisplay 60, such as display 22 (FIG. 1). A detailed schematicillustration of the control circuitry appears in FIGS. 4A, 4B, 4C, 4D,4E and 4F, it being noted that the user interfaces 50, cookingtemperature sensors 54 and induction heating assembly 56 for only onecooking location are shown.

Preferably, the induction heating assembly 56 includes an induction coil26 which is powered by switching power and control circuitry whichprovides a train of AC pulses having a frequency of about 22 KHz. Thecontrol circuitry, illustrated in FIGS. 4A-4F, includes a power circuit200, typically receiving a 220 Volt 50 cycle, electric mains input. Thepower circuit 200 comprises a bridge rectifier 202 and a pair ofcapacitors 204 and 206 providing voltage rectification. The junction ofcapacitors 204 and 206 is coupled via a high voltage relay 208 to one oftwo capacitors 210 or 212, which are in turn connected to the outer turnand the intermediate turn of induction coil 26.

Relay 208 is operative to adapt the induction producing apparatus of thepresent invention for use with cooking utensils whose bottom surfaceshave either high or low electrical resistance. When a cooking utensilhaving a bottom surface with high electrical resistance, such asstainless steel, is employed, the relay 208 connects the junction ofcapacitors 204 and 206 to an intermediate turn of induction coil 26, viacapacitor 212. When a cooking utensil having a bottom surface with a lowelectrical resistance, such as aluminum, is employed, the relay 208connects the junction of capacitors 204 and 206 to the outermost turn ofinduction coil 26 via capacitor 210.

The interior turn of the induction coil 26 is coupled via samplingapparatus 220 to the junction of two series connected transistorswitches 214 and 216, which are operative to provide a high frequencydriving voltage across the induction coil 26 and either of capacitors210 and 212.

First sampling apparatus 218 samples the mains current, while secondsampling apparatus 220 samples the peak current of transistor switches214 and 216. The sampled information from apparatus 218 passes throughcircuitry 221 to a voltage controlled oscillator 224 which increases itsoutput frequency as the sensed mains current increases.

The sampled information from apparatus 220 is processed by a currentdetector 226 and is used to select the switching condition of relay 208.It is appreciated that apparatus 220 is operative to determine whether autensil being heated by the induction heating apparatus of the presentinvention has a bottom surface with a high or low electrical resistance.In this way, the apparatus of the present invention is able todistinguish between, for example, utensils having stainless steel andaluminum bottoms and to be operative to safely and efficiently heat bothtypes of utensils.

According to an alternative embodiment of the present invention, relay208 may be eliminated and the apparatus of the present invention may bedesigned to operate only with utensils having either high or lowelectrical resistance bottom surfaces.

The sampled information from apparatus 220 is also supplied to circuitry228 and is employed for protecting circuit elements.

Circuitry 230 (FIGS. 4A and 4B) provides timing, induction heatingcontrol, motor control and display functions.

It is particular feature of the present invention that the circuitry ofFIG. 4C includes temperature sensors 54 which measure temperature bysensing the current flow passing through induction coil 26. Variationsin the current flow provide indications of variations in temperature.

Reference is now made to FIG. 5, which is a generalized flow chartillustrating the operation of the circuitry of FIGS. 4A-4F. As can beseen from the flow chart, upon turning on the system for a cookinglocation by operating switch 19, following system initialization andfault checks, the system determines if a utensil located at the cookinglocation has a bottom surface having high or low electrical resistanceand adapts the operation of the circuitry of FIGS. 4A-4F, such as bymeans of relay 208, accordingly. Alternatively, where the system isadapted for use only for utensils whose bottom surface has either a highor low electrical resistance, the system will operate only in thepresence of the appropriate type of utensil.

Normally the system will periodically check to ensure that the utensilhaving an indicated resistance has remained at the cooking location, inorder to prevent damage to the induction heating system or inefficientoperation thereof.

The system checks the desired temperature indicated by dial 21 andcompares it with the temperature indicated by the temperature sensingapparatus. The induction heating assembly is operated as appropriate.

The following subroutine may be employed at this stage:

1. Operate the induction coil 26 and measure the temperature every 10seconds until the predetermined desired temperature indicated by dial 21is reached;

2. When the measured temperature exceeds the predetermined temperature,such as 100 degrees Centigrade, shift to pulsed operation of theinduction heating generator (such as operation for one second followedby a 10 seconds interval) until the measured temperature falls below thepredetermined temperature and return to step 1.

According to an alternative embodiment of the invention, when themeasured temperature is less than the predetermined temperature, insteadof step 2, the induction heating apparatus may be operated continuouslyuntil a weighted temperature is reached, the weighted temperature beinggreater than the predetermined temperature, typically by a factor ofabout 1.2 times the difference between the measured temperature and thepredetermined temperature. Once the measured temperature reaches theweighted temperature, the induction heating apparatus is operatedaccording to step 2.

Additionally the system operates to monitor the remaining desiredcooking time and the ON status of switch 19. It provides for operationof the stirring device throughout cooking or as desired by the user.Upon termination of the desired cooking time, the induction heatingapparatus is turned off and the stirring is typically continued for agiven period and then terminated. Visual and/or auditory notification ofcompleted cooking may be provided to the user.

Reference is now made to FIGS. 8-15 which illustrate stirring apparatusconstructed and operative in accordance with a preferred embodiment ofthe present invention. The stirring apparatus including a stirringassembly, indicated generally by reference numeral 60, is illustratedmost clearly in FIG. 8.

Stirring assembly 60 is arranged for removable and automatic drivingengagement with stirring drive apparatus, which is illustrated in FIGS.11A and 11B, via coupling apparatus, indicated generally by referencenumeral 62. The coupling apparatus includes a first engagement portion120, which is described in detail in FIGS. 9A and 9B and which undergoesreciprocating rotation about an axis 64 and a second engagement portion66 having a polygonal engagement recess 68. Second engagement portion 66and recess 68 are arranged symmetrically with respect to axis 64 forrotation thereabout.

The stirring assembly 60 comprises an axle portion 70 including ahousing 72 and an internal drive shaft 74. Housing 72 is formed with aperpendicularly extending arm 73, which terminates adjacent a protrusion75, extending perpendicularly to arm 73.

Internal drive shaft 74 is formed at one end thereof with a polygonalengagement protrusion 76 which is configured to a mate with recess 68.At an opposite end thereof, drive shaft 74 is provided with a conicalgear 78. Conical gear 78 drivingly engages a corresponding conical gear80 which is fixedly associated with a first stirrer drive axle 82.

First stirrer drive axle 82 is seated within housing 72 and is providedwith a polygonal bore 84 extending therethrough for receiving the shaft86 of a stirrer 90. First stirrer drive axle 82 is also provided with adrive gear 92, which drivingly engages a first intermediate gear 94 on afirst intermediate axle 96.

Intermediate gear 94 drivingly engages a driving gear 98 which ismounted on an axle 100, which optionally can serve as a stirrer driveaxle, in which case it is formed with an appropriate bore. Driving gear98 drivingly engages a second intermediate gear 102 on a secondintermediate axle 104. Intermediate gear 102 drivingly engages a drivinggear 106 which is mounted on a second stirrer drive axle 108, whichalong with gears 94, 98 and 102 and axles 96, 100 and 104 is seatedwithin housing 72 and which is provided with a polygonal bore 109,extending therethrough, for receiving the shaft 110 of a stirrer 112.

It is appreciated that when two stirrers are employed, as illustrated inFIG. 8, stirring drive axles 82 and 108 are normally employed. When onlya single stirrer is employed, it is normally mounted onto stirring driveaxle 100.

Reference is now made to FIGS. 11A and 11B which illustrate stirringdrive apparatus useful in the present invention. A first motor 128 hasits drive shaft 130 coupled, via a gear 131, to a two stage reducingplanetary gear assembly 132, whose output drives a shaft 134 which isrotatably mounted into a housing 136.

Engagement portion 66 is spring mounted into shaft 134 for drivenrotation together therewith about axis 64 and permitting retraction ofthe stem 138 of engagement portion 66 into the interior of shaft 134against the urging of a spring 140.

A second motor 142 has its drive shaft 144 coupled, via a gear 145, to athree stage reducing planetary gear assembly 146, whose output drives ashaft 148 onto which is mounted a rotating drive arm 150. Rotatablymounted onto drive arm 150 is one end of a reciprocating crank 152 whoseopposite end is rotatably coupled to arm 154, which is mounted forrotation about axis 64 and is coupled to a sleeve 156 for driving arm121 in reciprocating rotational motion about axis 64.

As seen in FIG. 8, fixedly mounted to hollow shaft 164 isperpendicularly extending drive arm 121 onto which is fixedly mountedfirst engagement member 122.

Reference is now made to FIGS. 9A and 9B which illustrate a preferredembodiment of coupler engagement portion 120. The engagement member 122generally comprises a bifurcated cone whose center is slotted by a slot124 having inclined side walls 126.

Reference is now made to FIGS. 10A, 10B and 10C which illustrate stepsin the engagement of protrusion 75 with engagement portion 120. In FIG.10A, the protrusion 75 is shown alongside the engagement portion 120. InFIG. 10B, the protrusion 75 is shown at the top of engagement member122, adjacent slot 124 (FIG. 9A), as mounting arm 121 is bentcorrespondingly. FIG. 10C illustrates seating of the protrusion 75 inslot 124, such that rotation of the hollow shaft 164 about its rotationaxis 64, produces rotation of the entire stirring assembly aboutrotation axis 64.

It is noted that engagement of protrusion 76 in recess 68 and rotationof shaft 164 about axis 64 produce rotation of the individual stirrers90 and 112 about their individual axes of rotation.

Reference is now made to FIGS. 12-15 which illustrate the structure andoperation of stirrers in accordance with a preferred embodiment of thepresent invention. FIG. 12 illustrates a stirrer 90 having a shaft 86formed with a retractable retaining protrusion 180 at the top thereof. Acoil spring 182 may be disposed about the bottom portion of the shaft 86to sit on an enlarged shaft portion 184 whose top surface 186 defines aspring seat.

Extending downward from enlarged shaft portion 184 is a generally spiralstirring element 190 of increasing radius. The element 190 is relativelythin and its overall configuration is generally conical.

Disposed at a termination end 191 of the stirring element 190 is autensil contacting member 192, which rides along the inner surface of autensil during stirring. It is a particular feature of the inventionthat the stirrer is arranged to accommodate surfaces at varying anglesand distances from the axis of rotation 64 of the stirring assembly.

As seen in FIGS. 13A, 13B and 13C, the utensil contacting member 192 iscoupled to the termination end 191 by a connector which allows theutensil contacting member 192 to assume varying orientations relative tothe termination end 191.

FIG. 14 illustrates an alternative embodiment of utensil contactingmember 193 which defines a ball socket 195. Here the termination end 197of the stirrer is formed with a ball joint protrusion 199 which isarranged for rotatable seating in socket 195.

As seen in FIG. 8, when considering the two different rotationalorientations shown for stirrers 90 and 112, it is seen that when theoverall distance between the utensil contacting member 192 and the axis64 varies within given limits, the shaft 86 of the stirrer rises orlowers relative to the axis 64 in bores 84 and 109 respectively, againstthe urging of springs 182, if springs are provided. It is noted thatalthough the two stirrers 90 and 112 are shown in FIG. 8 to havedifferent rotational orientations, for the purposes of explanation,normally they operate in synchronization and both have the sameorientation.

Reference is now made to FIG. 15, which illustrates the pattern ofcoverage of an inner surface of a utensil 18. It is seen that therotation of the utensil contacting members covers generally the entiresurface of a major portion of the utensil, which normally is heated andthus prevents sticking and burning of food in engagement therewithduring cooking.

It will be appreciated by persons skilled in the art that the presentinvention is not limited by what has been particularly shown anddescribed hereinabove. It is appreciated that any combination of thefeatures shown in the drawings also may lie within the scope of theinvention. The scope of the present invention is defined only by theclaims which follow:

We claim:
 1. A domestic cooking system comprising:electromagneticinduction apparatus; and a utensil having a curved cooking surfacehaving a generally circular cross sectional configuration and alsocomprising stirring apparatus including: at least one stirrer arrangedabout a stirrer rotation axis and defining an attachment end and atermination end; and means for causing said termination end to move incomposite dual axis rotational motion along said curved cooking surfaceand including: means for rotating said at least one stirrer about saidstirrer rotation axis; and means for reciprocatingly rotating said atleast one stirrer about a reciprocal motion axis perpendicular to saidstirrer rotation axis.
 2. The domestic cooking system according to claim1 and wherein said stirrer has a generally screw-type configuration. 3.The domestic cooking system according to claim 1 and wherein saidstirring apparatus comprises stirring drive apparatus and a stirrer,said stirring drive apparatus including quick coupling apparatus forautomatically coupling the stirrer drive apparatus to said stirrer. 4.The domestic cooking system according to claim 1 and also comprising autensil contacting member mounted onto the termination end of saidstirrer and being selectably orientatable with respect thereto so as tocorrespond to the configuration of the utensil surface in engagementtherewith.
 5. The domestic cooking system according to claim 1 andwherein said utensil is formed of a metal having a high electricalresistance and defining a curved cooking surface and also comprising aheat transfer member, formed of a metal having a low electricalresistance, said heat transfer member defining a curved top surfaceengaging the underside of the curved cooking surface and a generallyflat bottom surface.
 6. A domestic cooking system comprising:a basedefining at least one cooking location and comprising electromagneticinduction apparatus including: an induction coil disposed generally inat least one plane and operative to generate electromagnetic flux; atleast one magnetic field conductor disposed in a plane extendinggenerally non-parallel to said at least one plane so as to directelectromagnetic flux generated by the induction coil to said at leastone cooking location; and a utensil having a curved cooking surfacehaving a generally circular cross sectional configuration and alsocomprising stirring apparatus including: at least one stirrer arrangedabout a stirrer rotation axis and defining an attachment end and atermination end; means for rotating said at least one stirrer about saidstirrer rotation axis; and means for reciprocatingly rotating said atleast one stirrer about a reciprocal motion axis perpendicular to saidstirrer rotation axis such that said termination end moves along saidcurved cooking surface.
 7. The domestic cooking system according toclaim 6 and wherein said stirring apparatus comprises stirring driveapparatus and a stirrer, said stirring drive apparatus including quickcoupling apparatus for automatically coupling the stirrer driveapparatus to said stirrer.
 8. The domestic cooking system according toclaim 6 and also comprising a utensil contacting member mounted onto thetermination end of said stirrer and being selectably orientatable withrespect thereto so as to correspond to the configuration of the utensilsurface in engagement therewith.
 9. The domestic cooking systemaccording to claim 6 and wherein said utensil is formed of a metalhaving a high electrical resistance and defining a curved cookingsurface and also comprising a heat transfer member, formed of a metalhaving a low electrical resistance, said heat transfer member defining acurved top surface engaging the underside of the curved cooking surfaceand a generally flat bottom surface.
 10. For use with a utensil having acurved cooking surface having a generally circular cross sectionalconfiguration, cooking apparatus including apparatus for heating theutensil and stirring apparatus comprising:at least one stirrer arrangedabout a stirrer rotation axis and defining an attachment end and atermination end; and means for causing said termination end to move incomposite dual axis rotational motion along said curved cooking surfaceand including: means for rotating said at least one stirrer about saidstirrer rotation axis; and means for reciprocatingly rotating said atleast one stirrer about a reciprocal motion axis perpendicular to saidstirrer rotation axis.
 11. Apparatus according to claim 10 and whereinsaid stirrer has a generally screw-type configuration.
 12. Apparatusaccording to claim 10 and wherein said stirring apparatus comprisesstirring drive apparatus and a stirrer, said stirring drive apparatusincluding quick coupling apparatus for automatically coupling thestirrer drive apparatus to said stirrer.
 13. Apparatus according toclaim 12 and wherein said stirring drive apparatus comprises means forproviding first and second rotary drive outputs.
 14. Apparatus accordingto claim 10 and also comprising a utensil contacting member mounted ontothe termination end of said stirrer and being selectably orientatablewith respect thereto so as to correspond to the configuration of theutensil surface in engagement therewith.
 15. Apparatus according toclaim 10 and wherein said cooking utensil is formed of a metal anddefines a curved cooking surface and also comprising a heat transfermember formed of a metal, said heat transfer member defining a curvedtop surface engaging the underside of the curved Cooking surface and agenerally flat bottom surface.
 16. Apparatus according to claim 15 andwherein said cooking utensil is formed of a metal having a highelectrical resistance and said heat transfer member is formed of a metalhaving a low electrical resistance.